Three things degrade a dried spice: heat, light and moisture. All three are easy to control and all three are routinely ignored once a shipment has been signed for and moved into storage.
Heat accelerates the loss of volatile oils, which is the same loss that over-aggressive drying causes, only slower. A warehouse that reaches forty degrees in summer will quietly strip months of shelf life from material that arrived in excellent condition.
Light does the same to colour, particularly for anything red or green. Material stored in clear packaging near a window will fade visibly within weeks, and a faded product is discounted whatever its aroma.
Moisture is the one that turns a quality problem into a safety problem. Dried goods are hygroscopic: they will pull water out of humid air until they reach equilibrium, and at that point mould becomes a question of when rather than whether. Sealed packaging and a dry room are not optional.
None of this needs expensive equipment. A cool, dark, dry room with the goods off the floor and sealed will hold a spice close to the condition it shipped in.
